Problem 160 - Objective Biology for NEET

Question

Assertion: Sharks are said to be ammonotelic animals. Reason: Sharks can retain considerable amounts of ammonia in their blood.

Step-by-Step Solution

Answer

Sharks are ammonotelic animals. The reason correctly explains the assertion, as sharks can retain considerable amounts of ammonia in their blood due to their adaptations.

Step 1: Understanding the terminologies.

The term 'ammonotelic' refers to animals that excrete ammonia as the main end product of nitrogen metabolism. Nitrogen metabolism generally deals with the break down and utilization of proteins in the body. Ammonia is highly soluble in water, hence it is excreted largely by aquatic animals.

Step 2: Investigating the assertion and reason

The assertion states that sharks are ammonotelic animals. This is true, as sharks, like many other fish, primarily excrete nitrogenous waste in the form of ammonia, which is directly released into the surrounding water. The reason is that sharks can retain considerable amounts of ammonia in their blood. This is also partially correct, because, unlike mammals, sharks have adaptations that allow them to tolerate a relatively high blood ammonia concentration.

Step 3: Conclusion

The assertion and the reason both stand correct and the reason accurately explains the assertion. Sharks are indeed ammonotelic, and their ability to retain considerable amount of ammonia in their blood is related to their ammonotelic nature.

Key Concepts

Ammonotelic Animals

Ammonotelic animals are fascinating creatures due to their unique method of excreting waste. These animals primarily excrete nitrogen waste in the form of ammonia. This process is part of their nitrogen metabolism, where proteins are broken down in the body, resulting in ammonia as a byproduct. The term "ammonotelic" specifically refers to this distinct method of waste elimination.
Ammonia is highly soluble in water, which makes it an ideal substance for excretion by aquatic animals. This solubility allows them to easily eliminate ammonia into their watery environments without the need for complex waste storage mechanisms. In fact, you will find that many aquatic creatures, including some fish and invertebrates, adopt this method due to its simplicity and effectiveness in an aquatic setting.
For ammonotelic animals, maintaining a steady flow of water over their gills helps to continuously remove the ammonia from their systems, ensuring it is swiftly diluted and dispersed in the surrounding water. This method is energy efficient and particularly suited to animals living in water-rich environments, where the swift dilution of waste is easily achieved.

Sharks

Sharks are intriguing examples of ammonotelic animals. Unlike terrestrial vertebrates, sharks have developed specific adaptations that enable them to thrive with ammonia as their primary waste product. Sharks belong to a group of fish known as elasmobranchs, which also includes rays and skates. This group is characterized by their cartilaginous skeletons.
One unique adaptation that assists sharks in managing their nitrogenous waste is their ability to tolerate higher concentrations of ammonia in their blood. Sharks have efficient gill and kidney functions that assist in excreting ammonia. This feature allows them to regulate their body fluids and maintain osmotic balance with seawater.
Additionally, sharks possess an ability to reabsorb urea, another nitrogenous waste product, which helps manage waste production efficiently. This reabsorption also supports their buoyancy control and osmotic balance, crucial for their survival in marine environments.

Ammonia Excretion

The process of ammonia excretion is a vital aspect of maintaining homeostasis in ammonotelic animals like sharks. Due to ammonia's toxic nature, these animals have developed specialized systems to ensure its immediate removal.
In an aquatic environment, ammonia (NH3) produced from protein metabolism is directly released into the surrounding water through the gills or other permeable surfaces like skin. This process is effective because ammonia is readily diffused into water due to its solubility and low concentration in water helps to minimize toxic effects.
Furthermore, the lack of a need for conversion to less toxic substances, such as urea or uric acid, makes ammonia excretion a less energy-consuming process. However, this means that ammonotelic animals must remain in environments where water is plentiful to dilute and disperse the ammonia effectively.

• Aquatic environments provide a constant water flow to aid this process.
• Solubility of ammonia ensures dispersion without harming the animal.
• Efficient excretion and quick dilution prevent toxicity in the animal's system.

In summary, ammonia excretion is an elegant solution adopted by ammonotelic animals, allowing them to efficiently manage nitrogen waste in their aquatic habitats.